In a mobile communication system, a mobile station performs wireless communications within an area covered by a base transceiver station (BTS). The area covered by a base transceiver station is called a cell, and the size of the cell varies from big to small. Note that in the following description, a cell is a concept that includes a sector. Depending on the size of the area that the cell covers, the cell, in general, can be classified as follows: a macro cell that covers an area with a radius of an order of several tens of kilometers; a micro cell, whose coverage area is smaller than the macro cell, that covers an area with a radius of an order of several kilometers; a pico cell, whose coverage area is further smaller than the micro cell, that covers an area with a radius of an order of several hundreds of meters; a femto cell, whose coverage area is further smaller than the pico cell, that covers an area with a radius of equal to or less than several tens of meters; etc. The femto cell covers a relatively narrow area such as a building or a specific place. However, the femto cell according to the present invention, not depending on this kind of classification, refers to an area that any base transceiver station a user is able to install or relocate (a femto base transceiver station or a femto cell base transceiver station) covers.
FIG. 1 shows a situation in which femto cells and macro cells are mixed. A base transceiver station of a femto cell (femto BTS) transmits a signal with lower power compared to a base transceiver station of a macro cell (macro BTS) so that the femto cell, in general, covers a smaller area than the macro cell. The macro cell base transceiver station is systematically introduced to each area for establishing an area not by an ordinary user but by a specific operator. On the other hand, the femto base transceiver station, in addition to being less expensive compared to the macro base transceiver station, is capable of being easily installed or relocated by the ordinary user.
One of the advantages of the femto cell is that it can improve the area. For example, an area in a dead zone can be easily improved. Because a macro base transceiver station transmits a signal with relatively strong power, once the macro based transceiver station is installed, there occurs a possibility for a neighboring cell to receive interference. On the other hand, because transmission power of a femto cell is low, the interference between the cells is not so much a concern as it is in the case of the macro cell. Therefore, compared to a macro base transceiver station, a femto base transceiver station is easier to be introduced and is especially advantageous for improving an area in a dead zone. Another advantage of the femto cell is off-loading, which is achieved by moving a part of traffic in the micro cell to the femto cell. Therefore, it becomes possible for a user to receive excellent services by promoting the use of the femto base transceiver station.
In the meantime, a user sometimes performs communication which uses location information of the base transceiver station. Such communication includes a case where a user performs emergency communication. The emergency communication is communication with a police station, a fire station, etc. When a user makes a call for emergency communication and an emergency communication signal reaches a network through a base transceiver station, the network identifies an appropriate communication station (corresponding police station, fire station, etc.,) based on the location information of the base transceiver station and transfers the emergency communication signal to the communication station. In the case where the base transceiver station is a macro base transceiver station, the location information is controlled by an operator and an appropriate communication station can be selected. On the other hand, in the case where the base transceiver station is a femto base transceiver station, there occurs a problem. The reason is that regarding the femto base transceiver station, it can be easily relocated by the user. For example, suppose that, in the case where a femto base transceiver station installed in the first location is relocated in the second location which is far away from the first location, the operator is not aware of the second location after the relocation. If the user makes a call for emergency communication through the femto base transceiver station relocated in the second location, then the operator selects a communication station based on the first location before the relocation and the emergency communication signal ends up being transferred to that communication station. In this case, the user ends up talking with an inappropriate communication station (police station, fire station, etc.) which is geographically far away from the user and it is a concern that it will take time before the user is able to talk with an appropriate communication station.
One of the methods for dealing with this kind of problem is to prevent the user from relocating freely even if it is a femto base transceiver station. A method can be considered, for example, to make a hole on the wall and fix the femto base transceiver station. This method may solve the above problem accompanying the relocation, but it will, in addition to creating a limitation in installation location of the femto base transceiver station, increase the possibility of a user rejecting the installation of the femto base transceiver station and create a problem of preventing the promotion of the femto base transceiver station.
Another method for dealing with the problem accompanying the relocation is to automatically determine the location after the relocation in order to prevent the emergency communication signal being transferred to an inappropriate communication station. This technique is described in Patent Document 1. In the case of this method, the femto base transceiver station after the relocation performs scanning around and reports a list of neighbor macro base transceiver stations to an upper control apparatus (femto RNC), and the upper control apparatus identifies the location of the femto base transceiver station (FIG. 2, paragraph 0025, etc., in Patent Document 1)